Broken 1.15mm diam tip - removal from alloy

[edholly]

Managed to break the tip off a tiny No1 HSS centre drill in a piece that had about an hour and a half invested in it. Was the last of the 4 PCD holes for the muff on the 60 degree Vee twin I am building and was within a second or two of withdrawing the drill - always the way.

Certainly learnt from this to clear the drill frequently and also to go very slowly into the alloy.

Tried a 2mm drill but that just wanted to go to one side of the piece broken off - and blunted the drill of course.

Thought about it over night. The bolt hole was for a 4:40 cap head. Decided to try drilling out the unthreaded shank of a 4:40 bolt without the head and putting some teeth on the end with a 3 sided file. Put this in an ER16 collet and gave it a go.

Pretty much straight away the "mini holesaw" cut its way past the broken piece and then the broken piece disappeared amongst the "holesaw-ed" material ... Another centre drill inserted and taking utmost care the centre hole was finished and when drilled out and relieved for the cap-head 4:40 bolt all evidence of the initial problem disappeared.

Put this in here as it may help someone in the future ... Probably saved me an hour ... not that so much but hate redoing things !

Photos show :- the cap-heads bolted home - can't tell which was the offending one plus the broken centre drill ... the tip exposed inside the hole ... the mini holesaw -
Ed

 

[Swifty]

Good save there Ed, I will keep that method in mind in case it happens to me.

Paul.

 

[AussieJimG]

That's clever Ed, I like it.

Jim

 

[rcfreak177]

Great idea there Ed, Thanks for that, one for the memory bank.

Baz.

 

[Woodster]

Good Save, but could you not have just flipped the part over and drilled through from the other side? The broken pilot would just fall out with little or no fuss. May be a bit of a pain re-indicating, but would have been much quicker.

 

[edholly]

Woodster,

Thought about that but hitting a 1mm target 22mm away right in the middle after going through multiple layers was beyond what I thought was possible. So in the end decided to try the process above which worked surprisingly well.

Whenever you hurry a job you always risk an error as happened here .. I was heading off with a mate to look at a Mk2 Zephyr I told him about 120km away, but had a half hour and was trying to complete the 2nd muff on the rotary table using the 1st one's set-up on digitals etc .. and was within a few seconds of success drilling the centre holes when it broke. Anyway he bought the Zephyr, making it no.4 in his collection. He's just done Targa Tasmania in one and seen 195kph a few times with it.

Here's a photo of the muffs - damned if I can tell which hole it was now !

Thanks for the replies guys ... hope this helps someone out one day ..

Ed

 

[AussieJimG]

According to Wikipedia (and who could doubt that as a source) production of the Mk2 Zephyr ceased in 1962 and it had a top speed of 88mph (142kph). So the one that did 195kph has been heavily modified; as I remember the vehicle, it would need a bit of work on the brakes (drums all round ) and suspension before I would feel safe in it at that speed).

Jim